As is known, in a vehicle, the passengers sit in seats arranged in longitudinal columns and transverse rows. When the vehicle is set up for long trips, said seats may optionally be convertible into beds to improve the comfort of passengers by allowing them to lie down. However, where this is done, the rows of seats must be widely separated from each other (by around two meters) to allow said convertible seats to be opened out in the longitudinal direction. This greatly reduces the number of seats available in the vehicle.